Tokamaks are a very promising option to exploit nuclear fusion as a programmable and safe energy source. A very critical issue for the practical use of tokamaks consists of the power flow required to initiate and sustain the fusion process, in particular in the poloidal field coils. This flow can be managed by introducing a DC energy storage based on supercapacitors. Because such storage may be the most expensive and largest part of the poloidal power supply system, an excessive size would cancel its potential advantages. This paper presents innovative strategies to optimize the DC storage in poloidal power supply systems. The proposed solution involves the sharing of the DC storage between different coil circuits. The study is supported by novel analytical formulas and by a circuital model developed for this application. The obtained results show that this method and the related algorithms can noticeably reduce the overall size of the storage and the power exchange with the grid, providing a practical contribution toward the feasibility and the effectiveness of nuclear fusion systems.

The parallel connection of interleaved H-bridges (HBs) is widely used in high-current, low-ripple applications, such as particle accelerators and nuclear fusion systems, to handle the high-energy requirements and the four-quadrant functioning of the power converters. This parallel HBs approach leverages low-power-rated semiconductors, while the interleaving technique offers output current ripple cancellation. The connection of a generic number of parallel HBs sharing a common DC- bus is indicated as the common DC- bus configuration (CDC), whereas the configuration with galvanically isolated DC-buses is referred to as the split DC- bus configuration (SDC). This paper investigates both CDC and SDC topologies and compares the HB currents, the RMS of the HB currents, the RMS of the non-zero frequency component of the HB current, and the associated losses of the power converter. Specifically, the RMS of the non-zero frequency component of the current in CDC, which differs from that in SDC due to the presence of circulating current, is validated experimentally over specific sets of parallel HBs and gain ratios. The normalization of the RMS current in CDC is discussed to decouple the effect of the circulating current from the output current. Highlighting the advantages and disadvantages of CDC and SDC, an algorithm is proposed to automatically select the most appropriate topology for the power converter. The functionality of the proposed algorithm is demonstrated through illustrative design cases and validated numerically under varying system parameters and algorithm inputs, highlighting its robustness and adaptability.